When the age of the high-speed digital signal communication comes, the transmission of the high-speed digital signal plays an important role. Besides the increasing demand of operating frequencies and frequency bands of signals, the trend of precision designs of technology products also leads to the increasing of layout densities of print circuit boards. Therefore, problems related to signal integrity, electromagnetic interference, electromagnetic compatibility or power integrity during the signal transmission appear. The most significant one of the problems which are related to the signal transmission is the effect of the common mode noise caused by the high layout densities of print circuit boards.